Anode support structure for electrolytic cells having a base of aluminum or magnesium and alloys thereof



Apnl 21, 1970 c. c. SILSBY, JR 3,507,772

ANODE SUPPORT STRUCTURE FOR ELECTROLYTIC CELLS HAVING A BASE OF ALUMINUM OR MAGNESIUM AND ALLOYS THEREOF Filed Dec. 18 1967 2 Sheets-Sheet 1 /NVENTOR CHRISTOPHER C kS/Lsax Me A TTORNE Y Aprll 1970 c. c. SILSBY, JR 07,

ANODE SUPPORT STRUCTURE FOR ELECTROLYTIC CELLS HAVING A BASE OF ALUMINUM OR MAGNESIUM AND ALLOYS THEREOF 3 Sheets-Sheet 2 Filed Dec. 18, 19s? A rromvsr United" States Patent 3,507,772 ANODE SUPPORT STRUCTURE FOR ELECTRO- LYTIC CELLS HAVING A BASE OF ALUMINUM OR MAGNESIUM AND ALLOYS THEREOF Christopher C. Silsby, Jr., 385 Walworth Drive, Euclid, Ohio 44132 Filed Dec. 18, 1967, Ser. No. 696,965 Int. Cl. C22d 1/02 US. Cl. 204-286 4 Claims ABSTRACT OF THE DISCLOSURE Improvement in the manner of supporting the anode elements in an electrolytic cell and particularly to the idea of employing a relatively lightweight, high conductivity metal matrix for positioning and supporting the anode elements within the cell such as aluminum, magnesium and alloys thereof.

BACKGROUND OF THE INVENTION The field of this invention relates to electrolytic cells for the production of halogen gas from brine solutions. In the type of cell under consideration an anode structure is positioned within the cell in spaced relation to a cathode structure all enclosed within a container that is filled with a brine solution. Electrolysis is carried out by conducting a flow of electrical current from the anode structure through the solution to a cathode structure and collecting the products of electrolysis including chlorine gas, hydrogen gas, and a caustic efiiuent. In the modern construction of this type of cell, wherein the tendency is to increase the productivity of the apparatus by impressing electrical energy across the cell in very high current flow or density, it has been found necessary to carefully control the positioning of the anode assembly with respect to the cathode assembly and to provide as many cathode-anode interfaces as is possible within the confines of the cell structures. This means that the spacing between the anodes elements and the corresponding cathode elements becomes a problem. In addition, one of the factors affecting the etficiency of the cell and the electrical loading thereof involves the electrical resistance drop across the cell. Part of this electrical resistance drop is encountered within the anode supporting structure and it is. to this aspect of the problem that this invention is primarily directed. There are however, additional objects to be achieved by this invention as will hereinafter appear.

The construction of anode bases for electrolytic cells of one general type under discussion has been given attention in the prior art. For example, in Stuart Patent No. 1,866,065 there is disclosed an anode base structure involving the use of lead or lead-alloy metal in which the lower ends of the anode elements are embedded; this patent also discloses that a copper bus bar may be cast into and also embedded within the base structure. It will be noted however, that to properly support the anode base, there is required a heavy concrete section which acts as a container for the base and supplies rigidity and strength to the lead matrix. As a result, the base of this cell has a heavy and bulky construction. Furthermore, due to the relatively poor conductivity of the lead matrix, the electrical current is not distributed uniformly throughout the base, so that the anodes in proximity to the copper electrode will in effect do most of the work of the cell resulting in non-uniform operation of the device and reduced efficiency. In an effort to overcome the shortcomings of the previously cited patent, the same inventor secured a Patent No. 2,370,087 covering a modification in the form of the base structure. In this latter patent, the heavy concrete construction for the base was replaced by the use of a formed steel plate to contain the lead matrix into which the base of the anode elements were cast or embedded. In addition, a series of lugs were welded to the base and extended into the matrix to key the anode supporting matrix to the sheet metal or steel retainer base, an extension of which provided the electrical connection to the anode assembly. It will be observed, however, that in this construction there are a number of interfaces, namely (1) that between the anode and the lead matrix and (2) that between the lead matrix and the lower steel retaining shell which latter acted as a conductor for the current. In such a construction it will be seen that if there be any corrosion at the steel-lead matrix interface, a source of high resistance to the flow of electrical current to the anode assembly would be introduced. In fact this is exactly what occurred and as late as 1956 the problem was pointed out and disclosed in Baker Patent No. 2,742,- 419 wherein a means of sealing the base member from the affects of the anolyte solution was the subject of attention. Patent No. 2,393,868, again in the name of Stuart, shows an alleged further improvement on the anode base structure involving the use of a heavy cast iron bottom retaining member that confines the lead alloy into which the lower ends of the anode elements are embedded. It is apparent that there has been continuing need for improvement of the base structure as is shown in the history of the art and it is to this further improvement that the present invention is directed.

SUMMARY The essence of this invention lies in the provision of an anode base assembly which is of relatively light weight construction, has good electrical conducting characteristics and is easily fabricated. The prior art has devoted considerable attention to the construction of the anode supporting structure for the reason that it is critical to the eflicient operation of an elecrolytic cell. One of the reasons for this is that the base structure is subject to severe conditions derived from chemical, electrical and mechanical agencies. This is especially so in installations in which very high current densities are employed and wherein the spacing between the alternate cathode and anode elements is reduced to a minimum. In order to convey the heavy current loads (in installations wherein greater than 30,000 amperes are impressed on a given cell) it is essential that the resistance to current flow be kept to a minimum so that the impressed voltage is likewise kept down. In the prior art forms of construction it was found feasible to provide a heavy base section that derived its rigidity and strength from a massive concrete body or in the alternative from a heavy cast iron base, and then use in conjunction with these base structures a relatively soft and low melting metal intended to support the fixed ends of the anode elements. Lead alloy was found to be most feasible both from a point of convenience and ease of handling. However, lead has three inherent shortcomings: 1) Its electrical resistance is fairly appreciable, (2) its physical strength is low and (3) it is very heavy. In order to overcome the former, copper grids were embedded in the lead matrix to equalize the distribution of current throughout the lead matrix so that the anode elements remote from the source of electrical energy (the bus bars) were supplied with current to the same extent as the anode elements proximate to the center of the structure where the main bus bar was generally embedded. These copper grids also had the eifect of strengthening the lead matrix, but generally an additional rigid and strong supporting member was required. Furthermore, due to the inherent low strength of the lead alloy, the gripping action of the alloy upon solidification about the ends of the anode elements was less than desired. As a result, the anode elements were not in fact rigidly supported and tended to work loose either due to mechanical vibration or to other causes and resulted in a weakened joint; such condition naturally led to subsequent erosion at that point due both to the action of anolyte reaching such areas and/or the development of high resistance interface due to arcing or localized electrolytic action at those points. In addition the high specific gravity of the lead or lead alloys made the problem of handling the bases especially difiicult and burdensome. Furthermore, in the use of lead there is always the possibility of toxic by-products being produced which are extremely undesirable in an industrial installation wherein a large number of cells are employed.

To overcome the above disadvantages and shortcomings the subject invention comprehends the use of a lightweight metal such as aluminum or magnesium or their alloys as the matrix metal, into which the ends of the anode elements are positioned and cast. This type of material having in addition the characteristic of high electrical conductivity accomplishes other desirable ends. Primarily, the use of an alloy from the group of aluminum alloys or magnesium alloys reduces the resistance drop for the current in its passage through the matrix or base member. Thus, the comparison of the electrical conductivity of lead and its alloys against these properties of aluminum and its alloyand magnesium and its alloys is given in the following table:

TABLE-COMPARISON OF PHYSICAL AND ELECTRICAL PROPE RTIES Specific resis- Melting tivity, Tensile point, microhms/ strength, Specific Material F. cmfi p.s.i. gravity Commercial lead. 621 25 2, 000 11 Lead, 10% Sn 575 4, 000 10 Aluminum, as east. 1, 220 2. 8 8, 500 2. 7 Aluminum 1% Cu,

alloy -1, 000-1, 100 3 20, 000 2. 85 Aluminum +4% Mg,

alloy .1, 100-1, 200 3 23, 000 2. 6 Magnesimn, as east... 1, 205 4. 13, 000 1. 7 Magnesium+Al,

alloys 1, 100-1, 200 4. 0 25,000 1. 8 Copper, coml 1, 981 1. 6 35,000 8 9 By use of material that affords this reduction in electrical resistance, higher amperage can be impressed upon the cell. Again, the table illustrates a comparison of the strength characteristics of aluminum and magnesium alloys with the lead and lead alloys previously employed. Reference to this table will illustrate the advantage of employing the material of this invention as a matrix. For example, the strength of the aluminum alloy enables the anode supporting base or structure to be comprised entirely of this alloy without the need for additional strengthening or rigidifying structures as required by the prior art devices. This of course, simplifies the base design and its fabrication. It also results in a further advantage to be derived from the use of a matrix material which readily conveys electrical energy: in the first place it eliminates the need of embedded current distributing elements such as the previously used copper grids, while still insuring adequate distribution of current to all portions of the anode base so that each anode element receives its proper amount of electrical energy, and secondly, the use of a strong, electrically conducting base material simplifies the manner in which current is impressed on the cell. Thus the matrix material of my invention can be provided with an extension that acts as the bus bar connection to the source of external power. This is in distinction to the certain of the prior art structures wherein there had to be an embedded element such as a copper bar of high current carrying ability that would provide the bus bar connection. Certain of the above cited art illustrates the problem that had been encountered in the past in securing a proper electrical bond between the matrix material and the supporting base which acted as the carrier of current from the external source to the anode assemblyit being noted that unless this bond was carefully made (by the expedient of tinning or the use of embedded lugs integral with the supporting base) the resistance across this interface would be objectionable, making it impossible to operate e cell under high impressed current.

By way of illustration, using the comparative values from the above table, it can be shown that a row of nine (9) conventional graphite carbon anode sticks set in a mass of 28 lbs. of aluminum alloy has the same current carrying capacity as a similar row set in 1000 lbs. of lead. The substitution of some of the lead by the use of a copper grid is effective to provide better current carrying capacity and distribution but the high specific gravity of copper militates against weight saving that can be effected by the use of aluminum.

A further factor argues in favor of the use of a high conductivity-low weight base material, and that is the salvage aspect. Thus, the use of relatively expensive metals as copper and lead (in the amount required) dictate that such materails shall be salvaged and reused. This means that it is most economical (and practically necessary) that the fabrication of the anode supporting structures be carried out at the site of the electrolytic work. However, with the substitution of aluminum or like materials, the spent material used in the base can be scrapped; this allows the bases to be fabricated at points remote from the site of the electrolytic work.

Finally, fabrication of the anode supports in accordance with this invention, permits greater latitude in the choice of base size and shape, leading to a modular construction and permitting practically unlimited increase in the size of the electrolytic units.

BRIEF DESCRIPTION OF THE DRAWINGS I will now describe a preferred embodiment of my invention, having reference to the following drawings or figures in which:

FIGURE 1 is a side elevational view, partially in section, of an electrolytic cell incorporating my improved anode support structure or base, and

FIGURE 2 is a plan view along line IIII of the cell of FIGURE 1 with parts of the structure shown in section,

FIGURE 3 is an elevational or end view, partly in section, taken along line III-'III of FIG. 2. This view illustrates the fact that the anode bus connections are integral with, and a part of, the base metal that supports the anode elements.

FIGURE 4 is an isometric fragmentary sectional view of the anode base on a slightly enlarged scale to illustrate details of the construction. The anode elements are shown embedded in the matrix material before the grouting cover is applied.

FIGURE 5 is a somewhat schematic view to illustrate the principle involved in rigidly supporting the anode elements in a select configuration and immersing the ends of the elements in the molten matrix which is subsequently solidified to support the elements.

FIGURE 6 is a simple schematic sketch showing the application of this invention to an electrolytic cell of the mercury cathode type wherein the anode elements are suspended from the support srtucture or base.

DESCRIPTION OF A PREFERRED EMBODIMENT With reference to FIGURE 1, my improved base structure 2 is shown incorporated in a diaphragm type electrolytic cell 1. It forms the bottom closure for the cell, acting to support anode elements 3 mounted in a conducting matrix 4 which has a grout covering 7 that is laid over an intermediate, electrically non-conducting coating 6 such as epoxy resin, phthalic resin, asphalt, bitumen or like material. This base structure 2 supports an intermediate shell member 8 generally known as the cell can that in turn forms the intermediate portion of the electrolytic cell 1 and supports the cathode assembly. Enclosing the top of the cell is a cover member 20.

As is usual practice in the construction of diaphragm cells, the can 8 is formed with open bottom and top portions but has an enclosing hollow peripheral wall comprised of an outer panel 10, an inner peripheral panel 11, and upper and lower sections 12 and 13, respectively, all welded together to form a peripheral chamber 15 into which certain products of the electrolytic process are discharged, as will appear. The long side sections 11a of inner walls 11 are provided with vertical openings 25 about which the ends of the conventional hollow cathode sections are 16 are welded. These cathode sections 16 are generally fabricated in the shape of an elongated tube to extend across the cell from wall to wall; they are made from wire mesh material upon which is overlain an asbestos or other semi-permeable membrane 17. Thus, the inner walls 11 support the hollow cathodes 16 in such manner that the interior of the latter communicate at their ends via openings 25 with the chamber 15.

The end sections of peripheral wall 11, designated 1112 as seen in FIG. 1, may be constructed in the form of a half cathode wherein they are perforated and treated with the membrane material 110 in order that they shall act as a cathodic surface in the same manner as the surfaces of the full cathodes 16; in this respect they are known as half cathodes. Communication with the catholyte compartment 15 is had through openings 11d in wall 11. In the diaphragm cell, during electrolysis of brine the products of the reaction formed within the cathode sections 16 are caustic soda solution and hydrogen gas; both of these products are discharged into the catholyte chamber 15. This chamber is provided with outlets 18 and 19 for the collection of these products, respectively.

As is Well understood in the art, the space within the cell can interior (i.e. that space surrounded by the peripheral wall) is generally designated the anode compartment 22; it is that space surrounding the cathode elements 16 which is occupied by the anode elements 3 as will appear.

The cell 1 has a top cover member 20 which sits on the upper wall section 12 of the cell can 8 and is provided with a seal 21 in the form of a masticoating or other material to close the anode compartment 22 from atmosphere. Generally this cell cover is of dome shape and is constructed from concrete or other like inert material and is provided with a nozzle 23 that permits brine to be fed into the anode compartment 22 where it blends into the anolyte 9 within the anode compartment and replenishes the brine consumed in the electrolytic process. A second opening or nozzle 24 through the roof of the cover member 20 permits the anode gases (which may be chlorine or other halogen gases) to leave the chamber 22. Electrical energy is supplied to the cell 1 from a source of direct current 46 through electrical conductors 47 and 48 which connect, respectively, with base bus connection 5 and shell connection 49 (FIG. 3).

The entire cell assembly 1 is supported on blocks 30 which permits access to the bottom area of the cell in order to allow the cell to be moved into or out of the assembly line. It is understood that cells of this nature are arranged in groups or in rows to comprise a bank of such structures receiving power and raw brine from a common source and delivering the products of the cell to an appropriate collection system, not shown.

The representations herein will illustrate the manner in which the anode and cathode elements are closely packed but yet spaced from each other within the confines ot the cell. The purpose of such close packing is, of course, to increase the working area within the cell. To accomplish this end it is essential that the anode elements 3 be carefully and rigidly positioned by the base structure 2 so that when the cathode assembly (which comprises essentially the cell can member 8 that carries the several cathode elements 16) is put in position over the cell base 2, the anode members 3 are accurately spaced from the associated cathode members '16. It is essential that there be no contact between the cathode and anode surfaces; this would create a short circuit and cut oif the electrolytic action within the cell. My invention affords the means for properly positioning the anode elements 3 in the base 2.

As will be seen in FIGS. 3 and 4, the anode base is comprised of a metallic matrix 4. In this invention the metal chosen for the matrix is from the class of metals of relatively light weight having high electrical conductivity characteristics and reasonably high strength values. Representative of the metals of this group are aluminum and magnesium and the alloys of each of these principal metals. Herein lies the distinct improvement afforded by this invention compared with the prior art wherein commerical grades of lead were employed as the base material, Reference to the above table will clearly indicate the distinguishing differences in the properties of the two materials-that is, the materials of this invention compared to the materials conventionally used in the art prior to the conception of my invention.

In fabricating the base structure 2 of this invention, the anode members are first positioned with respect to one another on a pattern that assures the necessary spacing required by the cathode assembly (FIG. 5). For this pun-pose spacing blocks 45 may be clamped between the anode elements 3 and held in place by applied force F. The matrix metal 4 is heated to melting in a suitable container 40 by means of an appropriate heat source 41. Container 40 is shaped at 42 (FIG. 4) to provide an extension 5 which acts as an electrical connection point, as will appear. After the anodes 3 have been positioned with respect to one another, the assembly is lowered a distance x into the molten bath 4a of the composition hereinbefore described to such depth that the lower ends of the anodes 3 are immersed a substantial distance into the bath. Then said molten bath 4a is allowed to cool so that the matrix metal solidifies around the lower ends of the anode members 3 and firmly binds them into the matrix. The melting point of the metals of the class under consideration lie within the range of 1000-1250 F. It has been found that subjecting the anode elements to the higher melting temperatures of my class of matrix metals is conducive to driving off the absorbed and occluded gases in the lower ends of the elements and results in a very tight and efficient grasp on the anode when the metal 4a solidifies. This is in contradistinction to the prior practice wherein the anode sticks were not properly conditioned at the lower melting temperatures of convenventional matrix metals resulting in poor joints. Whereas in FIG. 5 the matrix material is shown as being heated within a container 40 by use of a heating device 41, it is also contemplated that the matrix material may be brought to molten condition in a separate crucible or furnace and cast about the ends of the anode members in a mold from which the solidified matrix 4 is then ejected or removed with the anodes positioned therein.

Because my class of matrix metal is chosen in part for its high strength characteristics, the base 2 is self sustaining without the need for internal reinforcement or any external support (as might be alforded by an enclosing container). It will thus be seen that the anode base assembly of this invention requires no supplemental members either in the form of current carrying grid network or a rigidifying and current carrying bus bar member of material, different from the matrix. As was pointed out above, in the use of the soft low strength and low conductivity lead alloys that was practiced prior to the concept of this invention, it was necessary to use a high conductivity Supplemental grid in the base structure in order to get proper distribution of the current. Also it was necessary to strengthen the base structure by way of reinforcement to prevent distortion of the base and consequent misalignment of the anode elements. Since the material chosen as the matrix metal of my invention is of light weight, the thickness of the base can be increased to afford additional strength and also to permit the ends of the anodes 3 to be inset in the matrix 4 a substantial distance, thereby affording lample support for said anodes. Furthermore, the lower faces of my base can be formed with ribs or corrugations to secure the necessary rigidity and also to facilitate the dissipation of heat generated in the electrolytic process.

As stated above, during the casting-in process, it has been found desirable to permit the lower ends of the anodes 3 to be immersed in the liquid metal for a reasonable period of time in order to allow the gas evolved from the artificial treatment of the anodes to escape; after the ends of the anodes have properly cured, the matrix metal is allowed to solidify thereabout, forming a tight bond between the metal and the anode elements 3. Although the melting temperature of the proposed aluminum or like alloy matrix metal is somewhat higher than that of the previously used lead alloys, this works to an advantage in that the impurities are distilled out of the anode ends at the higher temperature and assure a tighter bond between matrix metal and anode elements. The curing time is a function of temperature, but at the 1000-1200 F. range it is less than minutes. Thus the preferred process involves immersing the ends of the anodes for about this time and holding the mass at the liquid temperature before cooling and solidifying the molten matrix 4a.

After the metal 4a has solidified about the base of the anode sticks or elements 3 the entire assembly can be treated with the chemically inert insulating coating 6 and thereafter the cement or concrete grout mixture 7 can be cast over the surface of the treated matrix to insulate the same from the effect of the anolyte solution.

This latter step is well covered in the prior art and forms no part of this invention.

Thus it will be seen that the practice of my invention assures a firm physical bond and highly desirable low resistance electrical path between the matrix metal 4 and the supporting ends of the anode elements 3. In addition the strength characteristics of the metal selected for my matrix material assures adequate strength of the base assembly so that warpage and distortion or settling and misalignment of the anode elements 3 is avoided and a carefully controlled spacing of the anodes is assured. This permits accurate spacing between cathode and anode so that maximum cell efiiciency is possible. Since the bus bar connections 5 can be cast integral with and a part of the matrix metal 4 (FIG. 4), which by its nature is a good electrical conductor, this assures a low resistance path for the current from the bus bars to the anode elements. Further, because the contact area between matrix 4 and the ends of the anode elements 3 can be made sutficiently large there is assured a low resistance current path from the matrix metal 4 into the anodes. Finally, since the mar-tix metal is of relatively light weight the whole process of fabricating the anode assembly is simplified and made easier as is the subsequent handling of the assembly.

As pointed out previously, the subject of my invention has application to the conventional mercury cathode cells. Thus, with reference to FIG. 6, there is schematically illustrated such a cell '50 of this type having a basin 51 to receive a layer of mercury 52 which is fed into the cell through inlet 53 and passes out of the cell through outlet 54. Through inlet 67 the cell 50 is supplied with a brine solution 55 in which are submerged carbonaceous anode elements 56 attached to current carrying conductors 57. These conductors 57 are suspended from a supporting structure 58 that acts as a cover for the cell. The supporting structure 58 herein serves the same purpose as the base member 2 of FIG. 2, namely, to fix the anode elements 56 in a predetermined pattern. As is customary in the mercury cell, the vertical positioning of the anodes 56 above the surface of the mercury '52, is effected by adjustment of an appropriate mechanism indicated at 5 9. A seal 60 closes the reaction chamber 51. The product gas is led out of the system through discharge opening 61. The supporting structure 58 is coated with an inert, electrical insulating coating 62. A source of electrical energy 63 furnishes current for the electrolysis through conductor '64 to the integral bus bar connection 65.0f the supporting structure 58; after passing through the cell, current returns to generator or source 63 via conductor 66. It is just as important that the anode elements 56 of this cell be securely and carefully supported as are the corresponding elements of the diaphragm cell; to this end, the use of my proposed material and form of support is equally well adapted.

The foregoing description is intended merely as an illustration of the presently preferred forms of the invention. It will readily occur to those acquainted with the art that minor modifications can be incorporated into the disclosed device and it is intended that the scope of the following claims cover all such modifications.

LI claim:

1. In an electrolytic cell wherein an anode assembly is employed in conjunction with a cathode assembly for the electrolysis of brine by the passage of electrical current from anode to cathode, an improved means for supporting a series of individfual anode elements, comprising a base structure of relatively lightweight, high electrical conductivity metal, said metal having been brought to molten condition, the ends of the anode elements placed therein and said metal thereafter cooled and caused to solidify whereby the elements are gripped in fixed position and with low element to metal electrical resistance, said metal selected from the group consisting of aluminum, magnesium and alloys composed essentially of aluminum and/ or magnesium.

2. A structure as defined in claim -1 wherein the base consists essentially entirely of the relatively lightweight, high electrical conductivity metal and the support of the anode element is due entirely to the frictional gripping of the ends thereof by the said solidified metal.

3. A structure as defined in claim 2 including a bus bar connector which is cast integral with and a part of the' base structure.

4. A process for making an electrolytic cell including an anode base wherein said cell comprises a series of anode elements alternating with a series of cathode members between which an electric current is applied while said anodes and cathodes are immersed in a brine solution, the improved process consisting of the steps of melting a lightweight, high conductive, high strength metal having a melting point in excess of 1000 F., said metal selected from the group consisting of aluminum, magnesium and alloys composed essentially of aluminum and/or magnesium, positioning the individual anode elements in spaced relation corresponding to that which is required in the cell structure to accommodate the cathode members, subjecting one end of the anode elements to the molten metal, holding said elements in contact with said metal for a limited period of time to permit the ends of said anodes immersed in said metal to approach the molten metal temperature, and thereafter cooling the molten metal below its solidification point while main- 9 taining said anode elements in the aforesaid fixed spaced relation and thereafter cooling the assembly to ambient temperature and releasing the temporary support for the anodes whereby said anodes are held in said solidified matrix in spaced apart relationship.

References Cited UNITED STATES PATENTS 10 8/1968 Bonfils et a1 204-286 4/1956 [Baker et a1. 204-266 JOHN H. MACK, Primary Examiner 5 S. S. KANT-ER, Assistant Examiner 

